For many years, the demand has been made to participate actively in avoiding refuse, more particularly to recycle useful materials contained therein. The continuously appearing press reports with respect to the subject of recycling have characterized this demand. However, and when examined closely, the press reports cannot hide the fact that, in many cases, there are no solutions for a recycling of materials. The main problem is a strict separation of materials in the case of plastics as well as in the case of metals or glass.
The German electronic scrap ordinance emphasizes recycling in the context of a dual system. Consensus has been achieved with respect to many groups of materials, however, that, for the most part, only down-recycling is possible, more particularly, use in alternate products.
In this context, it can be assumed that manufacturers of intermediate products for electrical components such as television tubes will be addressed with respect to recycling.
The glass of a television tube is of special concern because of its weight during recycling of television apparatus.
The reasons for the difficulties of recycling television glass will now be explained. Often, comparisons are presented to recycling in the glass vessel industry. The example is suitable to clarify the different conditions which are present for possible modes of recycling. The glass vessel industry in Europe has, for a long time, at least with reference to the different countries, a substantially unified glass composition as a consequence of making processing similar and having the same suppliers of raw materials. Differences with respect to the chemical composition of glasses from neighboring countries however make recycling of imported products difficult. The recycling quota in Germany lies on average at approximately 53%. An increase is only possible by a still stricter separation of colored glasses.
The differences of only a few percent in the chemical composition between imported and domestic products with respect to glass for making vessels make recycling difficult; however, these differences are much greater for television glass because the European manufacturers of tubes and apparatus are supplied with glass from all over the world. Also, and for various technical reasons, the differences in the chemical composition of television glasses are increased.
The differences in the transmission and color of the screen glass make matters even more difficult. Apparatus have been and are being offered having screens of different transmissions. If, in the manufacture of television tube glass, greater quantities of fragments with different transmissions are used, then the color of the glass in the melt trough can no longer be controlled. A sorting of television glass is however almost impossible. In no case can one assume glass to be strictly separated by type after a separation of the display screen and funnel because a multiplicity of different glass compositions is still present behind the screen glass and funnel glass obtained. The separation nonetheless makes sense because basically, lead containing glass and glass which is substantially free of lead is separated. With reference to the composition of the funnel glass, only slight differences have been determined from one manufacturer to the other. This affords the possibility to return glass in the direct loop with reduced risk. However, the spread of the composition only allows a very limited fragment admixture so that critical characteristics of the glass can be controlled within tolerances. The critical characteristics are, for example: X-ray absorption, color, transmission, sight errors, electrical breakdown strength and thermal expansion.
These characteristics are already influenced by changing the glass composition by a few tenth of a percent. A change of the thermal coefficient leads to stresses in the screen-funnel bond and endangers, for example, the implosion stability.
The requirements as to the constancy of the characteristics can only be satisfied when the glass is melted with clearly defined raw materials. With respect to its sequence and its control possibilities, the melting process is not comparable to the processing operation. Processing is characterized by rapid control of the dimensional stability and corresponding feedback when errors occur. The melting process is a lethargic process having a very long reaction time of approximately 40 hours starting from the weigh-in of the raw materials to the finished product. A control operation is therefore not possible. If a raw material is used, such as the recycled glass having a high spread and fluctuation in the composition, then the controllability of the process is reduced and therefore, inter alia, the reliability which the product must have.
The sorting possibilities of television tube refuse do not today correspond to the requirements necessary for a trouble-free melting process. The recycling use is therefore today only possible for a small portion of present day production.
Display screen glasses contain as essential constituents the following: SiO.sub.2, Al.sub.2 O.sub.3, BaO, Na.sub.2 O, K.sub.2 O and additional absorbing admixtures. In this way, the contrast of the television image is increased.
Depending upon the manufacturer of the apparatus and apparatus type, the display screen glass can exhibit a different spectral transmission so that a great many display screen glasses having different spectral transmissions are to be melted and stored.
The manufacture of display screen glasses having different spectral transmission takes place in that the glass, depending upon requirement, is either melted discontinuously from different raw material compositions sequentially in a crucible or in several crucibles simultaneously and continuously.
Fragments are added to the melt in order to melt the particular glass mixture easier and at lower energy cost and in order to also be able to economically reuse the fragments. The manufacture of a display screen glass with a spectral transmission which cannot be precisely defined is to be absolutely avoided. Only such fragments can be added which exhibit the same spectral transmission as the glass to be melted.
For this reason, fragments must be sorted according to spectral transmission and stored before adding to the glass melt. This is very costly.
A still more complex storage can be expected when a statutory requirement is imposed which requires the manufacturer to take back used apparatus and apparatus for which no service life remains. The manufacturers of cathode ray tubes will receive very different types of display screen glasses which, if they are to be used again for display screens, must be separately collected and separately stored at great expense.
Accordingly, satisfying the demand for new cathode ray tubes having different spectral transmission, on the one hand, and, on the other hand, to collect the used cathode ray tubes comprising different glasses and to separate therefrom that glass which can be reused, is associated with great complexity and high cost.